Shallow draft propeller nozzle

ABSTRACT

A nozzle for a ship propeller having an axis of rotation comprises an annular shroud having a diameter and is adapted to surround the propeller. The shroud extends along the axis of the ship propeller and has inner and outer surfaces forming a foil. The outer surface of the shroud has a truncating surface extending along at least one of a top or bottom thereof.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to ship propulsion in general and inparticular to a method and apparatus for permitting an increased ductedpropeller size for a given draft.

2. Description of Related Art

Many ships are propelled by propellers having airfoil shaped blades.Such propellers are typically rotated about an axis of a shaft to createthrust against the surrounding water. Many attempts have been made toincrease the efficiency of such propellers and to increase their thrustfor a given required input power from a motor or engine. One suchattempt has been to provide a shroud or nozzle around the propeller asis commonly known as a ducted propeller or Kort nozzle.

As illustrated in FIG. 1, an illustration of a conventional ductedpropeller is shown generally at 10 in which the propeller 12 is rotatedabout a shaft 14. The shroud or nozzle 16 surrounds the propeller toprovide the aforementioned increase of thrust and efficiency, especiallyat low speeds.

One difficulty with conventional ducted propellers is that the nozzle orshroud which surrounds the propeller increases the overall diameter ofthe propeller assembly. In the case of conventional or Kort Nozzle, theshroud may be substantially larger than the propeller itself so as tocatch as much water as possible thereby directing this additional waterto the propeller. Accordingly ships fitted with such ducted propellersmay have increased draft or may have the size of propellers that may befitted thereto limited by the depth in which the ship is to operate.Such size of the propeller which may be used thereby limits the thrustthat can be provided by the propulsion system for the ship.

SUMMARY OF THE INVENTION

The new truncated nozzle alleviates this problem, by allowing to fitwithin the same draft limit a larger diameter shroud and propeller,which will produce higher thrust, or conversely, allow for less powerand fuel consumption for the same thrust as conventional ductedpropeller.

According to a first embodiment of the present invention there isdisclosed a nozzle for a ship propeller having an axis of rotation. Thenozzle comprises an annular shroud having a diameter and is adapted tosurround the propeller. The shroud extends along the axis of the shippropeller and has inner and outer surfaces forming a foil. The outersurface of the shroud has a truncating surface extending along at leastone of a top or bottom thereof.

The truncating surface may be located on a bottom of the shroud. Thetruncating surface may be located a top of the shroud.

The truncating surface may be substantially planar. The truncatingsurface may be substantially horizontal. The truncating surface may beconvex having a radius of curvature of at least 10 times the diameter ofthe shroud. The truncating surface may be concave having a radius ofcurvature of at least 10 times the diameter of the shroud. Thetruncating surface may have a rounded edge with the outer surface of theshroud.

According to a further embodiment of the present invention there isdisclosed an apparatus for propelling a ship comprising a screwpropeller having an axis of rotation and a nozzle surrounding the screwpropeller. The nozzle comprises an annular shroud having a diameter andis adapted to surround the propeller. The shroud extends along the axisof the ship propeller and has inner and outer surfaces forming a foil.The outer surface of the shroud has a truncating substantiallyhorizontal surface extending along at least one of a top or bottomthereof.

The screw propeller may be rotated by a shaft. The shaft may extend froma hull of the ship. The shroud may be supported by the hull.

The shaft may extend from a pod suspended below the ship. The pod may berotatable about a vertical or close to vertical axis. The shroud may besupported by the pod.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention whereinsimilar characters of reference denote corresponding parts in each view,

FIG. 1 is a cross-sectional view of a conventional ducted propeller.

FIG. 2 is a bottom perspective view of an apparatus for propelling aship according to a first embodiment of the present invention.

FIG. 3 is a partial cross sectional view of the nozzle of FIG. 2.

FIG. 4 is a side view of the propulsion system of FIG. 2 supported by aship's hull.

FIG. 5 is a side view of the propulsion system of FIG. 2 supported froma rotating pod.

FIG. 6 is a detailed rear view of the nozzle of FIG. 2 having a concavetruncating surface.

FIG. 7 is a detailed rear view of the nozzle of FIG. 2 having a convextruncating surface.

FIG. 8 is a detailed front view of a propulsion system according to afurther embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 2, an apparatus for propelling a ship according to afirst embodiment of the invention is shown generally at 20. Theapparatus comprises a screw propeller 22 surrounded by a nozzle orshroud 30. The propeller 22 may be of any known type and size as desiredby a user for the required application. The propeller 22 is rotated andsupported by a shaft 24 having an axis of rotation 26.

The nozzle 30 comprises an annular member extending between leading andtrailing edges, 32 and 34, respectively along an axis 26 of thepropeller 22. The nozzle is formed between inner and outer surfaces, 36and 38, respectively forming a foil shape therebetween. It will beappreciated that any foil profile may be utilized for the nozzle.

With reference to FIGS. 2 and 3, the nozzle includes a truncatingsurface 40 extending across one or both of the top and bottom edges ofthe nozzle 30. The truncating surface 40 is positioned to extendsubstantially horizontally across the nozzle. The truncating surface 40may be spaced apart from the nominal diameter of the nozzle 30 by asetback distance 42 which may be selected to reduce the height of thenozzle as much as possible while still providing sufficient strength tothe nozzle. By way of non-limiting example, the setback distance may beselected to be between 10 and 100 percent of the nozzle foil profile. Asillustrated in FIGS. 2 and 3, it will be appreciated that the truncatingsurface reduces the overall height of the nozzle 30 therebycorrespondingly reducing the overall draft required for such a nozzleused with a propeller of a given size. Similarly, it will be appreciatedthat the reduced height of the nozzle 30 will permit a larger diameterpropeller to be utilized thereby providing greater thrust for a giveninput power to the propeller. It will be appreciated that the truncatingsurface 40 will slightly reduce the efficiency of the nozzle in thelocation of the truncating surface due to the disruption of the flowpath over the foil profile. However it will also be appreciated that thelarger nozzle possible for a given permitted draft will also provide anadditional thrust exceeding the losses due to the disrupted flow overthe truncating surface.

With reference to FIGS. 2 and 3, in a preferred embodiment, thetruncating surface 40 may be substantially planar although thetruncating surface may also be curved as illustrated in FIGS. 6 and 7.In particular the truncating surface 40 may be concave as illustrated inFIG. 6 or convex as illustrated in FIG. 7 with a radius of curvature 44.The radius of curvature is selected to reduce the thickness of the topand bottom of the nozzle 30 while preserving some of the foil profileand should therefore be selected to be large to provide as great aheight reduction as possible. In particular, it has been found that aradius of curvature of greater than 10 times the diameter of the nozzlehas been useful.

With reference to FIG. 4, the nozzle 30 may be suspended from andsupported by the hull 8 of a ship wherein the propeller 22 is locatedtherein at the end of a propeller shaft 24. In such embodiments, thetruncating surface 40 may be located at the bottom of the nozzle so asto present a substantially flat surface parallel to a bottom of theocean, lake, river or the like. It will also be appreciated that in suchembodiments, the top of the nozzle 30 may also include a truncatingsurface facilitating engagement with the hull 8 and permitting thenozzle and propeller to be located closer thereto. Optionally, asillustrated in FIG. 5, the nozzle and propeller may be supported by arotatable pod 50, such as by way of non-limiting example an azimuththruster. In such embodiments, the pod 50 may be suspended from the hull8 by a rotating member 52 which is rotatable about a vertical axis 54with respect to the hull as are commonly known. Similar to as set outabove, for such embodiments, the nozzle 30 may include either or both ofa truncating surface at the top or bottom thereof.

With reference to FIG. 8, according to a further embodiment thetruncating surface 40 may extend across the top or bottom of the nozzle30 at an angle relative to horizontal indicated generally at 60. Such anangle will facilitate matching a top truncating surface to the angle ofthe hull at that location. It will be appreciated that this will beuseful in locating the truncating surface and thereby the nozzle asclose to the hull as possible. Optionally, as illustrated in FIG. 8, thetruncating surface may be flared outwardly from the nozzle to preventdebris, for example ice, from jamming between the nozzle and the hull.As illustrated in FIG. 8, the truncating surface and the outer surface38 of the nozzle 30 may also have a curved surface 62 having a radiusgenerally indicated at 64. The radius may be selected to be between 5and 15% of the nozzle outer diameter.

While specific embodiments of the invention have been described andillustrated, such embodiments should be considered illustrative of theinvention only and not as limiting the invention as construed inaccordance with the accompanying claims.

What is claimed is:
 1. A nozzle for a ship propeller having an axis ofrotation, the nozzle comprising an annular shroud having a diameter andbeing adapted to surround said propeller, said shroud extending alongsaid axis of the ship propeller and having inner and outer surfacesforming a foil, wherein said outer surface of said shroud has atruncating surface extending along at least one of a top or bottomthereof.
 2. The nozzle of claim 1 wherein said truncating surface islocated on a bottom of said shroud.
 3. The nozzle of claim 1 whereinsaid truncating surface is located a top of said shroud.
 4. The nozzleof claim 1 wherein said truncating surface is substantially planar. 5.The nozzle of claim 1 wherein said truncating surface is substantiallyhorizontal.
 6. The nozzle of claim 1 wherein said truncating surface isconvex having a radius of curvature of at least 10 times said diameterof said shroud.
 7. The nozzle of claim 1 wherein said truncating surfaceis concave having a radius of curvature of at least 10 times saiddiameter of said shroud.
 8. The nozzle of claim 1 wherein saidtruncating surface has a rounded edge with said outer surface of saidshroud.
 9. An apparatus for propelling a ship comprising a screwpropeller having an axis of rotation and the nozzle of claim 1surrounding said screw propeller.
 10. The apparatus of claim 9 whereinsaid screw propeller is rotated by a shaft.
 11. The apparatus of claim10 wherein said shaft extends from a hull of said ship.
 12. Theapparatus of claim 10 wherein said shaft extends from a pod suspendedbelow said ship.
 13. The apparatus of claim 12 wherein said pod isrotatable about an axis.
 14. The apparatus of claim 12 wherein saidshroud is supported by said pod.
 15. The apparatus of claim 9 whereinsaid shroud is supported by said hull.